Summary of Work: The molecular genetics analysis of neoplastic conditions of the female reproductive organs including endometrial carcinoma, uterine sarcoma, breast carcinoma, uterine leiomyoma, and ovarian carcinoma are under study. Analysis of these cancers, particularly endometrial cancer has defined a subset that have the molecular genetic phenotype of microsatellite instability. Microsatellite instability in individuals with hereditary non polyposis colorectal carcinoma, is the result of inherited alterations in genes involved in DNA mismatch repair. Mutational analysis fails to find alterations of the HNPCC genes in many sporadic endometrial and ovarian carcinomas with microsatellite instability. Several candidate genes (based on sequence similarity to other mismatch repair genes) were analyzed for alterations in these samples. Of these, hMSH3, was found to be altered in several endometrial tumors and cell lines. Introduction of a normal copy of hMSH3 into a hMSH3 mutant cell line restored certain aspects of defective DNA repair and drastically reduced the microsatellite instability in this cell line.Introduction of hMSH6 also restored DNA repair phenotypes indicating that hMSH3 and hMSH6 share partly redundant functions. We have also identified cell lines defective in the hPMS2 mismatch repair gene and complemented its function by cDNA transfection. The hMSH3/hMSH6 and hPMS2 restored cells are being utilized to determine whether there is an interaction between the cell cycle machinery and mismatch repair. The DNA repair process requires cellular arrest at certain stages of the cell cycle known as checkpoints. Current research is focused on understanding how the mismatch repair system coordinates with the cell cycle machinery to stop cell cycle progression and allow repair following exposure to damaging agents. Also under study are regions of allele loss on chromosomes 1, 10 and 14 in endometrial carcinomas. Fine mapping of these regions may lead to the identification of genes involved in endometrial carcinogenesis.